1. Field of the Invention
The present invention relates to a toner and an image forming method.
2. Description of the Related Art
Recently, a system for forming color images based on electrophotographic system is used over a wide area covering use in office and light printings by virtue of its advantages in a fast printing speed and simplicity.
As the image forming method based on the aforementioned electrophotographic system, single component development systems using a single component developer solely composed of a toner are particularly preferably used because it needs no complicated configuration of the apparatus therefor.
Among color image forming method using a single component development system, a develop method using a non-magnetic single component development system is preferably used. In the non-magnetic single component development systems, one non-magnetic single component development system in which an electrostatic latent image formed on an electrostatic latent image carrier comprising an organic photosensitive material or the like, is visualized by a toner carried and transferred by a toner carrier to which a toner layer limiting member for limiting the amount of toner on the surface of the toner carrier is pressed, is utilized.
In the non-magnetic single component development system, because the toner is frictionally charged by the contact between the toner and the toner layer limiting member and/or the toner carrier, it is necessary to use a toner having an excellent frictional charging property, or to use a toner carrier capable of readily giving electric charge. It is also necessary to supplement the toner carrier with the toner consumed in the development, and to properly replace the toner which is remaining undeveloped on the toner carrier.
In order to satisfy these requirements, there is proposed a method of adding an electric charge providing material to a constituent of the toner carrier so as to add an appropriate charge provision property to the toner carrier (see Patent Document 1, for example), or a method of adding a specified electric charge providing material to a constituent of the toner carrier and of adding an external additive having a large particle diameter to an external additive for the toner (see Patent Document 2, for example).
Although the foregoing methods can successfully upgrade the charge provision property in the initial stage of use by improving constitution of the toner carrier, but raises a problem of causing changes in the surface property of the toner carrier due to abrasion or the like during a long-term use, and of consequently increasing changes in the charge provision property to the toner, is caused.
Moreover, in the case where a charge providing material having a strong influence on the constituents of the toner carrier is used, the toner strongly adheres to charged points ascribable to the charge providing material, and this results in fusion or filming which are causative of conveyance failure or charging failure. This degrades the toner carrier, and consequently makes it impossible to keep a stable charge provision property for a long duration of time.
In addition, still another problem resides in that the toner carrier is prevented from attaining a stable toner supply property by the degradation thereof. Therefore, the toner carrier cannot appropriately supply and/or replace the toner in a suitable method because of a long duration of use, and this consequently produces development ghost in the resultant image.
Meanwhile, as for the toner, there are proposed methods of solving the above-described problems by adding an appropriate external additive to the toner particle (see Patent Documents 3 to 5, for example).
Only the simple addition of the external additive to the toner particle, however, cannot exclude influences caused by a long-term stress, and cannot fully solve problems in frictional charging property and in generation of the development ghost. Moreover, for the case where fluidity of the toner was improved by simply adding a large amount of external additive, a problem arises in that the external additive may adhere to the latent image carrier to thereby cause fusion or filming on the toner carrier, or may induce formation of scratches.
There are also proposed methods of using a spherical toner, which is so-called, suspension-polymerized toner, so as to keep an excellent fluidity of the toner, to thereby reduce contamination of the toner carrier (see Patent Documents 6 to 9). A simple spherization of the toner, which is merely caused by controlling the shape thereof so as to improve the fluidity, may be successful in giving an excellent fluidity to the toner, but is unsuccessful in providing an appropriate frictional charging to the toner, and this typically makes it difficult for a supply roller or the like to supply the toner in a stable manner to the toner carrier. This also makes it difficult to uniformly provide electric charge to a thin toner film formed on the toner carrier. This still also makes it difficult to stably control the amount of toner because of a low-temperature/low-humidity atmosphere in which the amount of toner supplied to the toner carrier is excessively increased beyond a controllable limit, and a high-temperature/high-humidity atmosphere, or the differences between a status after a long-term use and a status in the initial stage of use.
This consequently raises a problem that the toner remaining on the toner carrier after passing over the development zone cannot be recollected from the toner carrier, or a new toner cannot appropriately be supplemented. Further, the problem that the amount of charge of the toner on the toner carrier is non-uniform and the development ghost is produced, is caused.
In color image formation using a color toner comprising at least one of a yellow toner, a magenta toner and a cyan toner, together with a black toner, the color toner is generally consumed in a larger amount due to a large pixel ratio of the color image. When the fluidity is increased in order to improve the feeding property of the toner, the toner is easily scattered on the text portion. Consequently, the reproducibility of the text and image quality in repetitive copying are caused. This problem most likely occurs when the development is repeated over a long period.
Patent Document 1:
Japanese Laid-Open Patent Publication No. 7-281475
Patent Document 2:
Japanese Laid-Open Patent Publication No. 9-127783
Patent Document 3:
Japanese Laid-Open Patent Publication No. 10-20546
Patent Document 4:
Japanese Laid-Open Patent Publication No. 9-80911
Patent Document 5:
Japanese Laid-Open Patent Publication No. 2000-194161
Patent Document 6:
PCT International Publication No. WO00/13063
Patent Document 7:
Japanese Laid-Open Patent Publication No. 8-305074
Patent Document 8:
Japanese Laid-Open Patent Publication No. 10-333356
Patent Document 9:
Japanese Laid-Open Patent Publication No. 5-289405